Technical Field
The present invention relates to a control device for an internal combustion engine, and particularly relates to a control device for an internal combustion engine which is installed in, for example, a turbocharger-engine car.
Background Art
In a conventional internal combustion engine, a turbocharger is used in order to improve the output of an internal combustion engine (hereinafter, referred to as engine). The turbocharger is a device by which air is forcibly inputted to the engine in such a way that the turbocharger is mounted at an intake-air passage of the engine, and a turbine of the turbocharger is rotated by exhaust gas. There is a problem in the turbocharger that a supercharge pressure is increased more than necessary under a high rotational speed and heavy load condition, and the engine is broken, so that an exhaust-bypass passage is usually provided at an upstream of a turbine. A waste-gate valve (hereinafter, referred to as WGV) is provided at the exhaust-bypass passage. The exhaust gas flowed in an exhaust passage is flowed by the WGV, whereby an inflow of the exhaust gas passed through the engine is regulated. Thereby, a pressure in the intake-air passage is controlled at an appropriate level.
In general, the WGV is driven by a positive-pressure-type actuator. An intake air passage (upstream component of a throttle valve in which a pressure is particularly increased) is linked to a waste-gate actuator (hereinafter, referred to as WGA). Therefore, when a pressure in the intake air passage of the engine, which is driven in a supercharge mode or the like, is higher than an atmospheric pressure, the WGA can be operated. A relief amount of a relief valve connected to the WGA is regulated, whereby a pressure of an intake air, which is supplied to the WGA, is regulated, and an aperture of the WGV linked to the WGA is regulated. In general, a detector for detecting an activation amount of the WGA or the WGV is not mounted on the devices. Therefore, a detection value of a pressure, such as an intake-manifold pressure (hereinafter, referred to as Pb) at a downstream side of a compressor is used, whereby the relief amount of the relief valve is regulated. In a pressure condition where the WGA can be operated, the WGV, which is used as a bypass valve, is held at a totally-enclosed position by a mechanical component, such as a spring, which is installed in the WGA.
In general, a throttle valve (hereinafter, referred to as THV) provided at an intake air passage is operated, and an aperture area of the intake air passage is regulated, whereby the output of the engine is regulated. An intake-air mount passed through the THV can be controlled based on a physical formula by using the aperture area of the THV, an upstream pressure and a downstream pressure with respect to airflow, and a detection value such as temperatures at the upstream and the downstream of the THV. These technologies are generally used (for example, refer to Patent Document 1). However, in the technologies, a sensor for detecting the upstream pressure of the THV must be installed, so that there are problems in that a number of components is increased, and a cost of the control device is increased.
Therefore, a technology for suppressing the cost is described in Patent Document 2 which is previously applied by the applicant of the present application. A supercharge pressure (hereinafter, referred to as P2) sensor for detecting the supercharge pressure, which is a pressure at an upstream of a throttle, is not used in Patent Document 2. In Patent Document 2, an exhaust-gas amount is calculated by using a detection value of an intake-air amount and a detection value of a ratio of air to fuel, and the P2 is estimated by using a comparison result of a value, which is calculated by using a table that is previously set in accordance with the exhaust-gas amount, and a value which is obtained by adding the value being previously set to the Pb.